(1) Field of the Invention
The present invention relates to synergistic antimicrobial or biocidal compositions including a metal complex of a polyfunctional organic ligand and an isothiazolone. In particular the present invention relates to the use of monocopper (II) disodium citrate as the ligand and a 5-x-2-lower alkyl 4-isothiazolin-3-one wherein x is halo or hydrogen group as the isothiazolone including particularly mixtures of these isothiazolones.
(2) Prior Art
The prior art has described metal complexes of organic ligands as antimicrobial or biocidal compounds. These include U.S. Pat. Nos. 4,055,655 to Maurer et al 4,129,589 to Shringarpurey et al and 4,180,473 to Maurer et al. The process for their manufacture is described in U.S. Pat. No. 4,278,610 to Maurer et al. The problem is that these compounds are relatively poor antimicrobials and even large amounts provided protection for only a limited period of time.
The isothiazolones are described in U.S. Pat. Nos. 3,523,121 to Lewis et al; 3,761,488 to Lewis et al; 3,957,808 to Miller et al; 4,105,431 to Lewis et al; 4,243,403 to Lewis et al; 4,252,694 to Lewis et al; 4,265,899 to Lewis et al; 4,279,762 to Lewis et al. These are very superior antimicrobial agents; however, relatively large amounts are required.
Disodium monocopper (II) citrate (MCC) is particularly described as an antimicrobial compound by U.S. Pat. No. 4,055,655. Metalworking fluid (MWF) stabilizing activity is described in U.S. Pat. No. 4,129,509 (1978)). The former patent states that the compound is effective against microorganisms growing in alkaline environments (pH 8-12) due to the stability of the metal complex form only at high pH, with dissociation into toxic copper ions occurring upon encountering the lower pH (7.0) within microbial cells.
Studies on MCC have shown that it can temporarily inhibit the growth of Pseudomonas aeruginosa in laboratory media and transiently reduce the cell count in MWF contaminated with Pseudomonas spp. The use of MCC as a MWF additive is becoming more widespread and an improvement in its effectiveness was needed.
Although bacteria are highly important in the biodeterioration of MWF, fungi and yeast can play a major role as well, especially in the synthetic fluids (Bennett, E. O., "The Deterioration of Metal Working Fluids," Prog. Indust. Microbiol., 13, p 121 (1974)), (Rossmoore, H.W. and Holtzman, G.H., "Growth of Fungi in Cutting Fluids," Dev. Indust. Microbiol., 15, pp 273-280 (1974)). Fusarium and Cephalosporium are prominent fungal contaminants, and among the yeasts, Candida and Trichosporon spp. are often isolated. Fungi and yeast are known to be sensitive to the toxic effects of Cu ion (Hugo, W. B. and Russell, A. D., "Types of Antimicrobial Agents," in: Principles and Practices of Disinfection, Preservation and Sterilization, Russell, A.D., W. B. Hugo, and G. A. J. Ayliffe (Eds.), Blackwell Scientific Publications, Boston, p. 69 (1982)) and consequently the effect of MCC at high pH on a representative yeast, Candida tropicalis, was studied.
As a result of the machining operation itself, MWF can become contaminated with selectively large concentrations of soluble iron. The high stability constant of ferric citrate can allow exchange reactions between the ferric and copper ions in binding to the citrate ligand (Ashcroft, S. J. and Mortimer, C. T., Thermochemistry of Transition Metal Complexes, Academic Press, New York (1970)). Such reactions may destroy the antimicrobial activity of MCC in alkaline environments.
Kathon.TM. 886 is a commercial antimicrobial solution which is a mixture of 5-chloro-2-methyl-4-isothiazolin-3-one (8.6% by wt.) and 2-methyl-4-isothiazolin-3-one (2.6% by wt.). The mixture is very effective against bacteria, fungi and algae. The required dosages are sometimes ineffective in achieving the best results due to interfering nucleophiles in the metalworking fluids. The molecular species considered as nucleophiles in these systems are amines and sulfides, the former contributed by many metalworking fluid formulae and the latter from microbial activity. Thus, efficacy is a function of the metalworking fluid composition as well as the level of microbial contamination, nucleophiles from both competing for the isothiazolones.